A swash plate type compressor is typically used in an air conditioning system for a vehicle. The swash plate type compressor includes a plurality of pistons that are slidably fitted into a plurality of bores disposed in a cylinder block. A transmission of power is carried out as a swash plate secured to a rotary shaft rotates and causes the pistons to reciprocate in the bores. Reciprocation of the pistons causes suction, compression, and discharge of a gas.
Prior art swash plate compressors include a range of designs to transmit power from the rotating swash plate to the piston. One such design includes a swash plate having a slidably mounted pad on its surface. The pad contacts the outer surface of a spherical bearing that is operatively connected to the inner surface of a pocket of the piston. Alternate designs have been developed with the intention of using fewer components to reduce production cost.
One of these designs utilizes a shoe disposed on the face of the swash plate. The shoe includes a spherically shaped outer surface that fits into a concave pocket of the piston. This eliminates the need for the spherical bearing. Prior art compressors using the shoe design include a variety of materials to form the swash plates, the shoes, the balls, and the pistons. Problems associated with tribological mating of similar materials have necessitated that certain precautions be taken when selecting materials to form the components. One such precaution is the application of a solid lubricant coating between the metal components to avoid the mating of similar materials.
Metal coatings are commonly used to treat swash plate surfaces. U.S. Pat. No. 5,056,417 treats a swashplate body with a surface coating layer made of tin and at least one metal selected from the group consisting of copper, nickel, zinc, lead, and indium. U.S. Pat. No. 5,864,745 discloses flame sprayed copper based materials to coat swash plates.
Polymer based coatings have been suggested for coating aluminum swash plates, such as that disclosed in U.S. Pat. No. 5,655,432. The swash plate is treated with a coating of a mixture of cross-linked polyfluoro-elastomer bonded directly to the aluminum, a lubricious additive, and a load bearing additive such as boron carbide, for example. Polymer based coatings have less than desirable wear resistance due to soft physical characteristics, the polymer becomes even softer at higher temperatures.
The application of coatings increases the cost of production and the weight of the structure. The coatings can also reduce the strength of the compressor.
It would be desirable to produce a swash plate type compressor, whereby a cost of manufacture and a weight thereof are minimized, and a strength thereof is maximized.